Jensen et al U.S. Pat. No. 3,551,727 discloses a low work function composite surface for the collector electrode of a thermionic converter which comprises a refractory metal such as rhenium or tantalum. Gritton et al U.S. Pat. No. 3,558,935 discloses a number of series connected thermionic converters having mating protrusions extending from both the emitter and the collector surfaces.
Defranould et al U.S. Pat. No. 3,793,542 describes a thermionic converter structure which utilizes aluminum oxide insulation between the emitter and collector. Rason et al U.S. Pat. No. 3,843,896 teaches the use of a radioisotope fuel pellet that is enclosed in a capsule for an atomic diode battery or thermionic converter. The capsule has an emitter surface extending over substantially the entire capsule external area.